Lanthanum Derivative from “Tara” Tannin for Steel Temporary Protection

Abstract

Tannins are extracted from certain plants and contain numerous phenol groups. They may be employed, together with their derivatives, to formulate protective coatings due to their inhibitive properties. The objective of this research was to synthesize lanthanum “tannates”, to formulate washprimers. Two “Tara” (Caesalpinia spinosa) tannins and 0.1 M La(NO3)3 were employed to obtain the corresponding tannates. The inhibitive action of the tannates was evaluated by linear polarization and corrosion potential measurements employing a SAE 1010 electrode. Lanthanum tannates were used to formulate wash-primers whose anticorrosion performance was evaluated by corrosion potential and ionic resistance measurements. The primers were incorporated in alkyd paint systems and their anticorrosion performance was tested in the salt spray chamber and by electrochemical impedance spectroscopy. Lanthanum tannate primers protected steel and behaved in a similar way to that formulated with zinc tetroxychromate.